A new study of earthworm burrows finds:
Earthworm burrows provide not only the linkage between top- and subsoil for carbon and nutrients, but strongly increase microbial activities and accelerate soil organic matter turnover in subsoil, contributing to nutrient mobilization for roots.
- •Mechanisms regulate microbial activities in biopores vs. bulk soil, topsoil vs. subsoil.
- •Earthworms homogenize SOM quality in topsoil and subsoil.
- •Priming effect in earthworm burrows was 4–20 times higher than in bulk soil.
- •Biopores and bulk soil showed higher priming effect in subsoil than topsoil.
Priming effect is the change of soil organic matter (SOM) decomposition due to the addition of labile carbon (C) sources. Earthworms incorporate organic matter into their burrow-linings thereby creating preferred habitats for microorganisms, but the roles of such burrows in priming effect initiation is unknown. Here we study the mechanisms driving SOM decomposition in top- and subsoil biopores and additionally in the rhizosphere. Given the topsoil was newly formed after ploughing 10 months prior to sampling, we hypothesized that (1) SOM accessibility, enzyme activities and efficiency of enzymatic reaction (Ka) are main drivers of different priming effect in biopores vs. bulk soil and rhizosphere, subsoil vs. topsoil and (2) the production of microbial enzymes in biopores depends on microbial community composition. To test these hypotheses, biopores formed by Lumbricus terrestris L. and bulk soil were sampled from topsoil (0–30 cm) and two subsoil depths (45–75 and 75–105 cm). Additionally, rhizosphere samples were taken from the topsoil. Total organic C (Corg), total N (TN), total P (TP) and enzyme activities involved in C-, N-, and P-cycling (cellobiohydrolase, β-glucosidase, xylanase, chitinase, leucine aminopeptidase and phosphatase) were measured. Priming effects were calculated as the difference in SOM-derived CO2 from soil with or without 14C-labeled glucose addition.
Enzyme activities (Vmax) and the catalytic efficiency (Ka) were higher in biopores compared to bulk soil and the rhizosphere, indicating that the most active microbial community occurred at this site. Negative correlations between some enzymes and C:N ratio in bulk soil are explained by higher content of fresh organic C in the topsoil, and the corresponding C and nutrient limitations in the subsoil. The positive correlation between enzyme activities and Corg or TN in biopores, however, was associated with the decrease of C and TN with pore age in the subsoil. In the subsoil, priming effect in biopores was 2.5 times higher than bulk soil, resulting from the favorable conditions for microorganisms in biopores and the stimulation of microbial activities by earthworm mucus. We conclude that earthworm burrows provide not only the linkage between top- and subsoil for C and nutrients, but strongly increase microbial activities and accelerate SOM turnover in subsoil, contributing to nutrient mobilization for roots.
Related: Restoring Construction Soils with Compost, Earthworms and Plants – Permie Flix
The researchers used next generation sequencing of the DNA in soil from samples taken across the site that had a range of plantings between six and 10 years old.
The technique – high-throughput amplicon sequencing of environmental DNA (eDNA), otherwise known as eDNA metabarcoding – identifies and quantifies the different species of bacteria in a sample.
The researchers – students Nick Gellie and Jacob Mills, Dr Martin Breed and Professor Lowe – analysed soil samples at the restoration site at Mt Bold Reservoir in the Adelaide Hills, South Australia, and compared them with neighbouring wilderness areas as ‘reference sites’.
“We showed that the bacterial community of an old field which had been grazed for over 100 years had recovered to a state similar to the natural habitat following native plant revegetation – an amazing success story,” says Dr Breed, Research Fellow in the Environment Institute.
“A dramatic change in the bacterial community were observed after just eight years of revegetation. The bacterial communities in younger restoration sites were more similar to cleared sites, and older sites were more similar to the remnant patches of woodland.”
Revegetation rewilds the soil bacterial microbiome of an old field – Gellie – 2017 – Molecular Ecology – Wiley Online Library
Plant species diversity doesn’t improve soil
The above quote was left as a reply to a comment I’d left on a big ag research and education industry video talking about cover crops ages ago. It still irks me that these people are so ignorant.
Today I read the following study on plant species diversity’s impact on soil ecosystems, albeit in a conservation and restoration context that ends up restoring degraded agricultural lands these people create:
Restoring and managing for more diverse plant communities can improve recovery of belowground biology and functioning in predictable ways. Specifically, we found greater accumulation of roots, more predictable recovery of soil microorganisms (bacteria and fungal biomass), more rapid improvement in soil structure (less compaction), and less nitrogen available for loss from the system in prairie restored and managed for high plant diversity (>30 species) relative to the low diversity (<10 species) grassland plantings. Thus, the hypothesis that biodiversity promotes ecosystem functioning is relevant to large-scale conservation and restoration practices on the landscape.
Soil organisms have an important role in aboveground community dynamics and ecosystem functioning in terrestrial ecosystems. However, most studies have considered soil biota as a black box or focussed on specific groups, whereas little is known about entire soil networks. Here we show that during the course of nature restoration on abandoned arable land a compositional shift in soil biota, preceded by tightening of the belowground networks, corresponds with enhanced efficiency of carbon uptake. In mid- and long-term abandoned field soil, carbon uptake by fungi increases without an increase in fungal biomass or shift in bacterial-to-fungal ratio. The implication of our findings is that during nature restoration the efficiency of nutrient cycling and carbon uptake can increase by a shift in fungal composition and/or fungal activity. Therefore, we propose that relationships between soil food web structure and carbon cycling in soils need to be reconsidered.
Soil networks become more connected and take up more carbon as nature restoration progresses : Nature Communications